The invention relates to a cathode-ray tube comprising in an evacuated envelope an electron gun for generating an electron beam and a target which is scanned by the electron beam. The electron gun comprises a cathode unit having a cup-shaped cathode shank provided coaxially around the longitudinal axis of the electron gun. The end face of the shank extends perpendicularly to the axis. A cathode filament is disposed in the shank and an emissive body is provided on the end face. The cathode shank is suspended coaxially in a central aperture in a metal assembly plate by means of thin suspension rods. The plate extends substantially perpendicularly to the axis and is connected to the suspension rods. The assembly plate comprises apertures in which supporting pins extending substantially parallel to the gun axis are provided by means of insulation material. Connection lugs for the cathode filament are connected to the supporting pins.
Such cathode-ray tubes have a very wide field of application and are used, for example, as television camera tubes, television display tubes, oscilloscope tubes and the like. In a television camera tube the target often is a photosensitive layer, for example a photoconductive layer, on a transparent signal electrode, which is provided on the inner wall of a window closing the envelope. In a television display tube and an oscilloscope tube the target comprises one or more phosphors luminescing in different colours which are provided on the inside of the display window of the tube in the form of one or more layers or of a pattern of lines or dots.
Such a cathode-ray tube is disclosed in Netherlands Patent Application No. 8002343, corresponding to U.S. Pat. No. 4,403,169. In one of the embodiments of the cathode unit described in said Application the metal assembly plate is connected to one end of a cathode supporting cylinder. Said cathode supporting cylinder is connected in a cup-shaped control electrode by means of a glass ring and a metal cylinder. Such a construction is rather laborious. Moreover, the components used must be manufactured very accurately and a comparatively large number of welding points are used.
Positioning the cathode shank in the cathode unit and positioning the cathode unit in the cup-shaped control electrode are difficult operations because the cathode unit has no clear reference face which may be used as a starting point in positioning.